In my continued quest to make pleasant the festering pit of mud and children’s toys that is our garden, I’m building a 3.7m * 3.7m deck that will support an inflatable hot tub.

I’m just wondering what to use for risers – I’d thought about breeze blocks but am not sure how you can add small increments to the height of them?

Are those plastic adjustable risers strong enough for a temporary hot tub? They say they can take 1 vertical ton each but the manufacturer website suggests not suitable for spas (but perhaps they mean big permanent ones?)

I would be inclined to use a paving slab on a concrete foundation to spread the load and something like the already mentioned breeze block. Space out with plastic spacers as they go from 1mm to 10mm. Any more then use some wood. Remember there is going to be a lot of weight there so get the base well sorted.

I’ve just poked about the garden and it seems my plot is on more than a slope than I’d really thought it to be.

I know in theory I should probably use the posts in concrete , level then chop posts off method but I’d not accounted for that in my timber order and it’s also a fair size decking so would need extra supports?

Wondering whether I can just stuff the weed membrane down and hope I can get things level with breeze blocks?

Do it right the first time and it will last. Dig some holes, concrete some posts in, you’ll need the same amount of posts as concrete pads anyway to support the span of the 4×2 I’d dig them every 1.2-1.5m apart Level them up then bolt the joists to them.

Phone the timber supplier first thing in the morning, they may be able to add on some additional timber

Something to bear in mind is that (in England and Wales) you need planning permission for a deck if it’s more than 30cm above the ground. If it’s higher than that, and you have neighbours and 6 foot fences, they will see you walking about and realise you could see into their garden, and they’ll complain. Guess how I know.

Personally I’d go for 4×4 posts and 6×2 joists. I’d still use breeze blocks but wouldn’t consider them straight on the ground, level them up with a spirit level, pad of concrete underneath, then you can just build on top. If you want posts, dig the holes, build the frame with posts attached, pack out under the posts with stones etc. Get it level then pour in concrete around the posts, allow to set then plank it out. That way the posts are upright, in exactly the right place and the right height.

RRR, you don’t have to dig too much out at the top end. I built my neighbours deck like this, up slope it was a single breeze block on a pad, downslope it was up to 4, depends how much of a slope it was. We took some care putting the pads in, Trying to get their relative heights to in increments of a breeze block laid flat. When we built the stacks up we used the motar joints to fine tune the final heights and a 2m spirit level. It was worth getting that right as buildingbthe deck was then relatively straight forward.

The slope I guess (haven’t yet got any long timber to offer up) is 6” over a 4 metre drop.

I wouldn’t say I’ve much experience in these things so am looking for the simplest solution really!

The other challenge I have is that the soil at the top of the slope is full of hardcore from a previous owners patio and then bit at the bottom is softer and has a few old rotten tree stumps , just to make life more interesting …

So, does 16 concrete pads sound about right? I feel like there should be some clever way of getting the pads a similar height without using loads of breeze blocks on top!

if you’ve joists that are long enough then you could just do your 4 concrete pads in a row (or however many you want), put a breeze block on each one, lay the joist over all 4, pop a level on the joist, then wiggle them till the joist is level and resting on all 4 of them, the soft concrete at this point will allow the breeze block to move up and down a bit

The issue I’d forgotten about is that along the line of the fence (so a right angle) is a series of rotten stumps – some are solid and some soft. The plot is 4M * 4.1M but not perfectly square, hence my intention to put a 3.6M square deck on it and fill the edges with a decorative slate or something / plants.

The ground closest is solid and full Of gravel, soft and squishy next to the fence.

I’m really not sure I could get co concrete pads at the same level and indeed whether they’d subside?

I’d thought postcrete but that’s kind of meant to be lobbed in a hole and watered innit? Would it give a smooth enough top to put a block on or the joists themselves? Or would a quick drying concrete be better?!

Thanks all for the continued help and emotional support. I threatened to cancel the timber order and buy 2 bulk bags of plum slate earlier …. :-S

Cheapest, but more labour intensive, is to buy ballast and cement if your making concrete. Wickes sell it in 25kg bags so that makes it easy to gauge the ratio, 5 ballast bags to 1 cement bag Depends on the size of your hole but that we’ll probably do 2 or 3 pads easily.

Wtf are you mortaring with that? 5:1 is the most common mix, maybe 3:1 for pointing in exposed circumstances. 3:2 and you’ll get loads of problem with shrinkage, not to mention it costing triple what it should